(1) Field of the Invention
The present invention relates to a double walled storage tank. In particular, the present invention relates to a double walled storage tank primarily intended for the storage of hazardous materials. The tank comprises an internal tank substantially contained inside an external tank. A minimum number of internal supports are provided between the internal tank and the interior of the external tank to avoid interfering with the free flow of fluid through the interior of the external tank. The tank also comprises a pair of spill boxes. One spill box surrounds an access opening to the double walled tank and catches and retains any hazardous material that should spill when loading or unloading the tank through the access opening. A second spill box serves as a pump housing and catches and retains any hazardous material that should leak from the pump or the pump's fluid connection with the internal tank.
(2) Description of the Related Art
Prior art double walled tanks often comprise a first tank that is supported in the interior of a second tank by reinforcement members that are connected between the exterior wall of the first tank and the interior wall of the second tank. The reinforcement members are required to support the first tank inside the second tank in a spaced relation with the bottom of the first tank being supported above the bottom of the second tank. This particular type of construction is employed so that if any materials should leak from the first tank, they will be contained inside the second tank.
Prior art double walled tanks are also often constructed with the external tank having a sloped bottom wall. Should fluid leak from the first tank, it will gravitate over the bottom wall of the second tank and collect in an area of the second tank where a drain output is provided.
However, prior art double walled tanks employing reinforcements between the first internal tank and the second external tank are disadvantaged in that the reinforcements will often disrupt the free flow of fluid over the bottom wall of the external tank to the drain collection area. This is especially true in double walled tanks employing reinforcements that extend across the path of fluid flow to the drain collection areas of the tanks. This presents the possibility that hazardous materials that happen to leak from the internal tank will collect in areas of the external tank where the reinforcements prevent the free flow of fluid to the drain collection areas.
Prior art double walled tanks also often have pumps that communicate with the internal tank and several access openings in the tank for inputting materials into the internal tank or drawing materials out of the tank. The access openings are often provided with lids or caps that seal off access to the materials stored in the tank. With tanks employed in storing hazardous materials, very often the caps or lids that close the access openings of the tank are provided with locking mechanisms that prevent the unauthorized access to the hazardous materials contained in the tank. However, the pump connections and access openings of prior art storage tanks have been found to be disadvantaged in that, should hazardous materials leak from the pump connection or spill from the access openings when being input to the tank or drawn from the tank, prior art tanks provide no way of controlling or containing the leak or spill and preventing their spreading to other areas of the tank.